A reduction in an angular transmission error of a speed reducer is required for a variety of technical fields such as industrial robots and machine tools. Various control techniques have been proposed (cf. JP 2012-122509 A and JP 2003-223225 A) in response to requests for a reduction in the angular transmission error.
JP 2012-122509 A proposes usage of an encoder arranged on an input side of a speed reducer and another encoder arranged on an output side of the speed reducer to reduce an angular transmission error. JP 2003-223225A proposes usage of error correction data acquired in advance to reduce an angular transmission error.
Techniques disclosed in JP 2012-122509 A require a plurality of encoders. Therefore, there is a high manufacturing cost of a control device incorporating the techniques disclosed in JP 2012-122509 A.
Techniques disclosed in JP 2012-122509 A require the arrangement of the encoder on the output side of the speed reducer. On the other hand, there are technical fields in which the arrangement of an encoder on an output side of a speed reducer is not desirable (e.g. technical fields of industrial robots). Therefore, the techniques disclosed in JP 2012-122509 A face a problem in versatility.
Techniques disclosed in JP 2003-223225 A require preparation of the error correction data inherent in every speed reducer in advance. Therefore, the techniques disclosed in JP 2003-223225 A require a lot of labor of a user in the preparation and management of the error correction data.
According to JP 2003-223225 A, the error correction data is prepared without considering a change in an angular transmission error caused by a load. Therefore, the techniques disclosed in JP 2003-223225 A may not sufficiently reduce the angular transmission error under a condition in which a load is applied to a speed reducer. As just described, the angular transmission error causes poor follow-up accuracy for a track defined by command values.